1. Field of the Invention
The present invention relates to a pluggable transceiver module for releasable connection to a base unit in a computer network, and in particular a pluggable module which has power control circuitry which can be used to adjust the supply voltage supplied to at least a subset of components within the module. The invention also relates to a combination comprising such a pluggable transceiver module and a base unit into which it may be releasably connected.
2. Description of the Related Art
Pluggable transceiver modules are used extensively in large router and switching systems, in information storage systems, data communication networks, as well as other systems. It is usually intended that such modules are able to be inserted into the receiving interface for the module in the router or switch base unit without disrupting any other modules which may be connected to the base unit, or disrupting the base unit itself. However, many pluggable modules, and in particular those containing low voltage components with associated large capacitors, can, if not properly designed, draw a large amount of in-rush current at the moment of connection to a system. This large in-rush current can cause a momentary drop in the base unit power supply voltage, causing glitches in the power supply of the base unit into which the module has been plugged. Such glitches can cause other boards or modules connected to the unit to malfunction, and in a worst case can cause complete system shutdown. Such problems are known already in the art, and are described for example by Huat, C. L. “Low Voltage Hot Swap Controller With In-rush Current Control”, Linear Technology Magazine, May 2005, pages 17 to 19.
In addition, as well as causing problems in a unit into which a pluggable module is plugged, the large in-rush current which can occur can also damage components within the module itself.
As noted above, the problem of a large in-rush current causing power supply problems in the base unit into which a pluggable module is connected is known in the art, and prior solutions to this problem have been to provide dedicated chips, for example the LTC 4216, Maxim 5924 or Maxim 5918. For example, the LTC 4216 chip available from Linear Technology Corporation, 1630 McCarthy Boulevard, Milpitas, Calif. 95035-7417 provides for controllable in-rush current control by the provision of a “soft start” feature, which ramps a supply voltage Vout from 0 v to a required level for the supply of components provided on a board on which the chip is incorporated. Only the rate at which the voltage ramps upwards can be controlled using the LTC 4216, and no more complicated ramp-up profiles are supported. Moreover, the LTC 4216 has typically not been widely used in pluggable module applications, because it requires a relatively large area of PCB space for itself and its supporting components. The additional PCB space thus required can be very hard to accommodate in high density designs, which are almost always used for small pluggable modules. Typically, the LTC 4216 provides a power on voltage ramp of the supply voltage Vout over a time period of approximately 150 to 200 milliseconds.
Whereas the LTC 4216 chip is a dedicated chip aimed at the problem of reducing in-rush current when a board is inserted into a backplane, other less complicated chips are also available which provide a non-controllable voltage ramp feature on start-up, but which typically is performed too quickly to prevent the problems noted above. One example of such a chip is the LTC 3026 voltage regulator, again available from Linear Technology Corporation. The LTC 3026 is a voltage regulator chip which can be used to provide a low voltage supply to low voltage components. The LTC 3026 includes a built in, uncontrollable “soft start” feature, which ramps up the voltage Vout supplied from the regulator over a period of approximately 200 microseconds. However, this degree of start up ramp is often too short a time period to avoid the problems of in-rush current noted above.
The Multiple Source Agreements (MSAs) associated with optical transceiver modules such as XENPAK (see www.xenpak.org) also provide requirements such as the “Inrush current during hotplug”, which for XENPAK MSA Section 10.4 is listed as a maximum of 50 mA/ms.
Prior to the present invention, it has not been possible to meet such specifically defined requirements in pluggable transceiver modules.